The present invention relates generally to small burners for combustible gas designed for a maximum gas consumption rate of less than 60,000 BTU/hr., and more particularly to such a gas burner having a forced air draft, also known as a power burner.
In the gas burner art it has been the practice to use atmospheric burners in applications where a maximum gas consumption rate less than 60,000 BTU/hr. is desired. An atmospheric burner draws combustion air at atmospheric pressure into a mixing tube by the action of a stream of pressurized combustible gas flowing through an orifice at relatively high velocity into the mixing tube. The proper air-gas mixture is obtained by regulating the pressure of the gas and providing an air inlet aperture in the mixing tube which is sized to admit the proper amount of air in relation to the gas flow rate determined by the gas pressure and orifice size.
Atmospheric burners may be used either in an open area or in an enclosed space having a suitable exhaust flue, so long as the air surrounding the flame is relatively quiescent. Atmospheric burners do not perform well in the presence of turbulent ambient air, and are susceptible to being blown out under such condition. An example of an atmospheric burner used in an open area is the surface burner of a kitchen range. An example of an atmospheric burner used in an enclosed space is the burner of a conventional home heating furnace. In the first example the flame burns in the quiescent atmosphere of the typical kitchen and in the second example the flame is maintained in a relatively quiescent atmosphere by the use of a heat exchanger which separates the enclosed combustion compartment from the moving air passing through the heating plenum under the influence of the furnace blower.
Where it is desired to use a gas burner having a relatively large gas combustion rate on the order of several hundred thousand BTU/hr., it has been the practice in the gas burner art to use a power burner having a forced air draft. Rather than relying exclusively upon the flow of pressurized gas through an orifice to draw combustion air into the burner, a power burner is provided with an air blower to force combustion air into the burner at a rate in excess of that which could be drawn by a conventional atmospheric burner. Power burners, because of their relatively large gas and combustion air flow rates, typically generate a long torch-like flame which, if it is to burn in an enclosed space, is usually provided with a combustion chamber of sufficient size to permit the full length of the flame to be developed for efficient combustion. Large power burners are typically used in connection with large heating plants such as a steam boiler where there is no difficulty in providing a large combustion chamber.
In certain applications it is desirable to employ a small gas burner having a maximum gas consumption rate on the order of 60,000 BTU/hr. or less where the flame must burn in a relatively small combustion area in the presence of non-quiescent, circulating air, where the circulating air is used as a heat transfer medium. For reasons of efficiency and space limitation, the products of combustion of the burner are introduced directly into the circulating air without the use of a heat exchanger. An example of such a use is a food preparation oven having a chamber for receiving and heating food and duct means and impeller means for recirculating air in the chamber, where the gas burner is disposed in the path of the circulating air. Heretofore, small food preparation ovens having a maximum heat requirement of less than 60,000 BTU/hr. have employed electric resistance heating elements which suffer no deleterious effect from turbulent, high velocity air passing over them. For reasons of energy efficiency and economy, however, it would be desirable to replace the electric resistance heating elements with a gas burner. However, the only gas burners heretofore commercially available having a maximum gas consumption rate of 60,000 BTU/hr. or less have been atmospheric burners.
Atmospheric burners are unsuitable for use in an environment where the atmosphere surrounding the flame is non-quiescent and where the products of combustion are directly mixed with heated air for cooking food. Under such conditions, atmospheric burners either have their flames disrupted by the turbulence of the surrounding atmosphere such that clean combustion is not obtained or the turbulence of the atmosphere surrounding the burner periodically blows the flame out. Furthermore, accidental or intentional obstruction of the air circulating ducts of such a food preparation oven while in use can result in a transient change in the pressure condition of the atmosphere surrounding the burner such that an undesired pressure relative the burner is produced. This can cause a reversal of the direction of flow of the air-gas mixture in the burner, resulting in a back fire where flame exits through the combustion air inlet of the burner, causing a safety hazard condition.
In order to overcome problems associated with the use of an atmospheric gas burner in a turbulent atmosphere it would be desirable to employ a power burner where by virtue of the use of a combustion air blower a positive pressure condition could be maintained in the burner relative the combustion chamber of the oven at all times. It would further be desirable to provide such a power burner having an appropriate small heat output with a maximum of less than 60,000 BTU/hr. and preferably on the order of 40,000 BTU/hr. and which is of disproportionately smaller physical dimensions than conventional large power burners and having a disproportionately shorter flame. This would permit the burner to be located in a relatively small space and also permit the flame to achieve complete combustion within the relatively small combustion space available without being disrupted by intervening structure. A suitable small gas power burner is provided by the present invention.